1. Field of Invention
The present invention relates to a driver circuit and a method for driving a load circuit; particularly, it relates to a light emitting diode (LED) driver circuit and a method for driving LEDs, which require less number of circuit devices and are able to control LED brightness from the AC side.
2. Description of Related Art
Referring to FIG. 1, conventionally, to provide power to an LED circuit from an AC power supply, it requires an AC-DC power regulator 10 to convert an AC voltage to a DC voltage, and an LED driver circuit 20 to provide electrical power to the LED circuit 50 and control current through the LEDs. Besides a transformer, the AC-DC power regulator 10 further comprises a primary side circuit 11, a secondary side circuit 12, and other discrete devices such as a capacitor C2, a diode D2, etc. The secondary side circuit 12 detects the output voltage and provides a feedback signal to the primary side circuit 11 by means of opto-coupling to control the operation of a power switch P in the primary side circuit 11.
The aforementioned prior art has the following drawbacks. Because it requires the AC-DC power regulator 10 to generate a regulated voltage and the LED driver circuit 20 to control current through the LED circuit 50 according to the regulated voltage, the prior art circuitry needs at least three integrated circuit (IC) chips: the primary side circuit 11, the secondary side circuit 12, and the LED driver circuit 20; this is not cost-effective. Besides, there is not a method to control the LED brightness directly from the AC side.
In view of the above drawbacks, it is desired to provide a driver circuit and a method for driving a load circuit.